Considering the complexities and particularities of each district heating (DH), RELaTED concept is being implemented in four different DH networks covering extremely different climatic conditions, construction traditions, urban density, pre-existing district scheme, ownership and energy services contract schemes:

Large district heating in operation in Belgrade, Serbia

The district heating network of Belgrade comprises 750km and delivers 3500GWh to approximately 50% of the city.

Belgrade is the capital and largest city of Serbia. Its urban area has a population of 1.34 million, while over 1.65 million people live within its administrative limits.

The city of Belgrade is served by the district heating operated by Beoelektrane. This network comprises 750km and delivers 3500GWh to approximately 50% of the city.

Within RELaTED, Beoelek will deploy the following conversion activities to the district heating network in Belgrade:

  • Low temperature conversion of one subnetwork comprising several households and apartment buildings with modern insulation levels. Tentative network temperature levels of ~50-55ºC are expected in this conversion.
  • Connection of heat recovery from waste incineration plant.
  • Connection of large solar heat production plant.
  • Construction of 20MW heat pump production plant. Heat source: River SAVA.
  • Connection of several reject heat producers from cooling applications.
  • Planning and tendering for the conversion for heat recovery and connection of a 1500MW electric power plant with an estimated heat output of 600MWt.
  • Promotion of adoption of  new technologies developed by customers and partners connected to the Belgrade DH network.

New urban development with associated ULT DH in Vinge, Denmark

Vinge is a green field development and the largest urban development project in Denmark. It’s designed as a green and smart city with a sustainable energy infrastructure. All buildings in Vinge must be low energy or passive houses and heated by renewable energy.

RELaTED will demonstrate its ULT DH system for new low-energy developments with large shares of renewable energy with the best possible fiscal solution for homeowners and district heating company and minimal environmental impact.

All buildings in Vinge must be low energy or passive houses and heated by renewable energy.

Vinge will demonstrate the scalability of the ULT DH concept for new urban developments, where grid design should adapt to steady increases in energy loads by connection and diversification of energy sources, particularly of renewable nature.

For this new urban development, 36 interconnected townhouses (with mandatory connection), and 23 detached houses (with voluntary connection) will be built. The district heating network is already established for all theses houses.

In the early stages of the district heating, heat will be provided by a 200kW air/water heat pump with two 1,500-liter water storage tanks and a 100kW inline electric heating element. In further development phases, other renewable energy supplies such as heat pumps, waste heat, solar thermal, biomass etc. are expected to be connected to the grid.


  • Within RELaTED, the DH system in Vinge will convert its LT DH system operational at 60/30ºC to the RELaTED 45/30ºC ULT concept.
  • Electric booster and DHRHP units will be used to guarantee that peak consumption periods are covered correctly while maintaining overall low operational temperature.
  • The integration of BILTST systems will be studied in several concept houses where the benefits of local solar thermal heat generation and injection into the grid will be evaluated.
  • Also within RELaTED, energy planning, extension of DH, connection of further RES, etc. will be performed in order to ensure the development of its low carbon DH concept over its 20 years deployment period.

DH in operation with large share of biomass in Tartu, Estonia

With over 90.000 inhabitants, Tartu is the second largest city of Estonia. Tartu is served by a district heating system privately owned and operated by Fortum Tartu and its subsidiary AS Keskkatlamaja. Yearly 500GWh are delivered to over 1500 consumers in the city, 94% of this energy is obtained from biomass and peat.

Main consumers are collective housing (49%), industry and commercial buildings (33%) and individual housing (18%), with 40-60 new connections to the grid per year.

94% of the energy delivered to Tartu consumers is obtained from biomass and peat.

Within RELaTED, Fortum will develop the following implementations:

  • ULT conversion of the TARKON-TUGLASE DH network area comprising 54 consumers totalling 4,3MW with a network length of 4.6 km. Technical limitations of the DH network will be investigated, and associated feasible technical and economically viable conversion scenarios identified.
  •  Development of a heat purchase strategy from one or several industrial waste heat producers with an estimated power of 0.5 to 1 MW.
  • Connection of excess heat from cooling applications to the DH network.
  •  Connection of waste heat sources and excess heat from bio CHP as heat sources for desiccant cooling plants in summer.

Corporate DH with mixed uses in Iurreta, Basque Country, Spain

Iurreta heat production system delivers space heating and domestic hot water to a set of building owned by the Basque Government.

Iurreta is located in the northern coast of Spain. The demonstration site consists on a set of buildings owned by the Basque Government The building complex hosts part of the emergency, rescue and fast intervention groups of the Ertzaintza (regional police of the Basque Country).

The campus is composed by a total of 14 multi-rise buildings with different characteristics and uses.  Heat needs in the complex are covered by means of a centralized heat production system with an installed total power of 650 kW, operative at 80/60ºC, which delivers space heating and domestic hot water.

In addition to centralized system, several independent heat pumps are used to serve a small subset of small buildings. Several buildings in the campus are equipped with cooling systems comprising chillers connected to fan-coil systems.

Within RELaTED, the following activities will be performed:

  • ULT conversion of the DH network, with LT conversion of heat delivery systems within buildings. Operation temperatures in the main distribution network will be adapted for at~40-45ºC. Distribution systems at buildings requiring higher distribution temperature will be fed by means of DHRHP to allow service temperatures in the range of ~50-55ºC.
  • Integration of 3FS and DHRHPs in buildings equipped with cooling plants.
  • Integration of BILTST system in South exposed walls.
  • Densification of the DH network with the connection of presently isolated HVAC plants.
  • Adaptation of control strategies to ensure maximum use of BILST and Heat pump capacity.

Feasibility studies

Within RELaTED, feasibility studies are being performed for the development of new district heating networks in already consolidated urban environments. These studies are conducted at regional scale, where regional energy agencies of the Basque Country (EVE) and Mazovia Energy Agency will identify:

  • industrial waste heat sources suitable of heat recovery,
  • possible renewable resources such as solar thermal,
  • and geothermal heat production capacity.

Considering this de-carbonized heat generation capacity, these studies will identified candidate urban areas of ULT DH systems. Also, the studies will incorporate technical and financial information about:

  • the cost of setting up heat delivery infrastructure,
  • capacity and cost estimation of additional backup heat sources,
  • development phases of the DH network, etc.

Additionally, an administrative roadmap will be developed to incorporate requirements related to the modification of energy, regional and urban planning documents to allow and support the installation of such an infrastructure.